Robots used for underwater exploration, etc. often move on the soft ground (including sandy soil and muddy soil) on the seafloor. Crawler robots are more suitable than wheeled robots for this kind of operations. In wheeled robots, wheels often dig deep into the soft ground, rendering the wheeled robots unable to move. On the other hand, crawler robots are generally free from such troubles thanks to low ground pressure.
A crawler robot includes left and right crawler devices. Each of the crawler devices includes front and rear wheels and an endless crawler belt run around the wheels.
The wheels and the crawler belt are engageable with each other for torque transmission. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2006-168661) discloses a crawler device including wheels and a crawler belt. Projections are provided in peripheral surfaces of the wheels. The projections are arranged in a circumferential direction equally spaced from each other. Engagement holes to be engaged with the projections are formed in the crawler belt.
When the robot disclosed in Patent Document 1 moves on the soft ground for underwater exploration, sand and/or mud may enter between the crawler belt and the wheels, resulting in undesirable events such as disengagement of the projections from the engagement holes that may cause the crawler belt to come off the wheels, damage and eventual breaking of the crawler belt and excessive tension acting on the crawler belt.
The undesirable events associated with the robot of Patent Document 1 mentioned above should basically be solved by engaging a crawler belt with wheels only by frictional force as disclosed in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2002-178962) and Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2004-276685). Detailed description of the crawler devices of Patent Documents 2 and 3 are given below.
In the crawler device of Patent Document 2, an annular groove is formed around a central portion of an outer periphery of the wheel and left and right portions of the outer periphery serve as receiving surfaces. Rigid engagement elements are formed in each of the receiving surfaces such that the engagement elements are arranged in a circumferential direction spaced from each other. On the other hand, the crawler belt is made of rubber. Engagement projections are formed around a central portion of an inner periphery of the crawler belt such that the engagement projections are spaced from each other.
The engagement projections of the crawler belt enter the annular groove of the wheel. At the same time, the inner periphery of the crawler belt contacts outer surfaces of the engagement elements of the wheel and bite into engagement grooves between the engagement elements. Thanks to these features, torque can be transmitted by frictional force only.
The engagement of the engagement projections with the annular groove prevents the crawler belt from being displaced from the wheel in the width direction, thereby preventing the crawler belt from coming off the wheel. Moreover, the engagement grooves also serve to remove sand and/or mud.
The crawler device disclosed in Patent Document 3 has similar features as the crawler device disclosed in Patent Document 2. Specifically, an annular groove is formed around a central portion of an outer periphery of the wheel and left and right portions of the outer periphery serve as receiving surfaces. First crawler grooves for facilitating frictional engagement are formed in each of the receiving surfaces such that the crawler grooves are arranged in a circumferential direction spaced from each other. On the other hand, the crawler belt is made of rubber. Engagement projections are formed around a central portion of an inner periphery of the crawler belt such that the engagement projections are spaced from each other. The engagement projections of the crawler belt are adapted to enter the annular groove of the wheel. Second crawler grooves for facilitating the frictional engagement are formed in left and right portions of the inner periphery of the crawler belt.